1. Field of the Invention
The present invention relates to an image forming apparatus, such as an electronic copying machine, having an original size detecting device for automatically detecting the size of an original on an original table.
2. Description of the Related Art
As is generally known, some electronic copying machines include a device for automatically detecting the size of the original to be copied.
In devices of this type, an original table upon which the original is placed is covered with an openable original cover. The inside of this cover is tinged with a color highly sensitive to a photosensitive drum. When the original is irradiated with light of a wavelength whose reflection factor for the color of the original cover is low, the size of the original is detected utilizing differences in the intensity of light reflected from the original and light reflected from the original cover. The length of the original in the scanning direction is obtained by moving a single detector underneath the lower surface of the table and detecting the point of change of the intensity of a reflected light beam.
In this case, however, the information for the original length with respect to the scanning direction is obtained from only the output of one detector. If an image of a color of a low-reflection factor exists on the original, the original may be mistaken for the original cover.